System and method for detecting rotating stall in a centrifugal compressor

Abstract

A system and method is provided for detecting and controlling rotating stall in the diffuser region of a centrifugal compressor. The process begins with the detection or sensing of acoustic energy associated with the onset of rotating stall. A pressure transducer is placed in the gas flow path downstream of the impeller, preferably in the compressor discharge passage or the diffuser, to measure the sound or acoustic pressure phenomenon. Next, the signal from the pressure transducer is processed either using analog or digital techniques to determine the presence of rotating stall. Rotating stall is detected by comparing the detected energy amount, which detected energy amount is based on the measured acoustic pressure, with a predetermined threshold amount corresponding to the presence of rotating stall. Finally, an appropriate corrective action is taken to change the operation of the centrifugal compressor in response to the detection of rotating stall.

1. A method for correcting rotating stall in a radial diffuser of a centrifugal compressor, the method comprising the steps of:
 measuring a value representative of acoustical energy associated with rotating stall in a radial diffuser of a centrifugal compressor;  
 filtering the measured value with a bandpass filter to obtain a filtered value;  
 rectifying the filtered value with a full wave rectifier to obtain a rectified value;  
 filtering the rectified value with a low pass filter to obtain a stall energy component;  
 comparing the stall energy component with a predetermined value to determine rotating stall in the radial diffuser, wherein rotating stall is present in the radial diffuser when the stall energy component is greater than the predetermined value; and  
 sending a control signal to the centrifugal compressor to adjust an operational configuration of the centrifugal compressor in response to a determination of rotating stall.  
 
   
   
     2. The method of  claim 1  wherein the step of measuring a value representative of acoustical energy associated with rotating stall includes the step of measuring an acoustic pressure in the radial diffuser of the centrifugal compressor with a pressure transducer. 
   
   
     3. The method of  claim 2  wherein the pressure transducer is positioned in a compressor discharge passageway. 
   
   
     4. The method of  claim 1  wherein the step of filtering the measured value with a bandpass filter includes the steps of:
 filtering the measured value with a high pass filter having a break frequency of 10 Hz to obtain an intermediate value; and  
 filtering the intermediate value with a low pass filter having a break frequency of 300 Hz.  
 
   
   
     5. The method of  claim 4  wherein the high pass filter is a single pole RC high pass filter and the low pass filter is a six order Butterworth low pass filter. 
   
   
     6. The method of  claim 4  further comprising the step of amplifying the intermediate value with a gain amplifier. 
   
   
     7. The method of  claim 1  wherein the full wave rectifier is an active full wave rectifier. 
   
   
     8. The method of  claim 1  wherein the step of filtering the rectified value with a low pass filter to obtain a stall energy component includes the steps of filtering the rectified value with a low pass filter having a cutoff frequency of 0.16 Hz. 
   
   
     9. The method of  claim 1  wherein the predetermined value is a multiple of the stall energy component calculated during normal operation of the centrifugal compressor without rotating stall. 
   
   
     10. The method of  claim 9  wherein the predetermined value is 2 to 6 times the value of the stall energy component calculated during normal operation of the centrifugal compressor without rotating stall. 
   
   
     11. The method of  claim 1  wherein the step of sending a control signal to the centrifugal compressor includes the step of sending a control signal to the radial diffuser. 
   
   
     12. The method of  claim 11  further comprising the step of adjusting a diffuser ring to narrow a width of a diffuser space in the radial diffuser in response to the control signal being sent to the radial diffuser. 
   
   
     13. The method of  claim 1  further comprising the step of amplifying the measured value with a gain amplifier. 
   
   
     14. The method of  claim 1  further comprising the step of conditioning the measured value to remove acoustical energies not associated with rotating stall. 
   
   
     15. A method for detecting rotating stall in a centrifugal compressor, the method comprising the steps of:
 measuring a value representative of acoustical energy associated with rotating stall in a centrifugal compressor;  
 performing a Fast Fourier Transform on the measured value to obtain a plurality of frequencies and corresponding energy values;  
 selecting frequencies and corresponding energy values associated with rotating stall from the plurality of frequencies and energy values;  
 summing the corresponding energy values of the selected frequencies associated with rotating stall; and  
 detecting rotating stall in the centrifugal compressor by comparing the summed energy values to a predetermined threshold value, wherein rotating stall is present in the centrifugal compressor when the summed energy values are greater than the predetermined threshold value.  
 
   
   
     16. The method of  claim 15  wherein the step of measuring a value representative of acoustical energy associated with rotating stall includes the step of measuring an acoustic pressure in a radial diffuser of the centrifugal compressor with a pressure transducer. 
   
   
     17. The method of  claim 16  wherein the pressure transducer is positioned in a compressor discharge passageway. 
   
   
     18. The method of  claim 15  wherein the step of selecting frequencies and corresponding energy values associated with rotating stall includes the step of selecting frequencies and corresponding energy values in a frequency range of about 10 Hz to about 300 Hz. 
   
   
     19. The method of  claim 18  further comprising the step of removing frequencies and corresponding energy values that are not associated with rotating stall from the frequency range of about 10 Hz to about 300 Hz. 
   
   
     20. The method of  claim 15  wherein the predetermined threshold value is a multiple of the summed energy values calculated during normal operation of the centrifugal compressor without rotating stall. 
   
   
     21. The method of  claim 20  wherein the predetermined threshold value is 2 to 6 times the value of the summed energy values calculated during normal operation of the centrifugal compressor without rotating stall. 
   
   
     22. The method of  claim 15  further comprising the steps of:
 generating a control signal for a radial diffuser of the centrifugal compressor in response to the detection of rotating stall; and  
 sending the generated control signal to the radial diffuser to alter a configuration of the radial diffuser.  
 
   
   
     23. The method of  claim 22  further comprising the step of adjusting a diffuser ring to narrow a width of a diffuser space in the radial diffuser in response to the generated control signal being sent to the radial diffuser. 
   
   
     24. The method of  claim 15  further comprising the step of amplifying the measured value with a gain amplifier. 
   
   
     25. The method of  claim 15  further comprising the step of conditioning the measured value to remove acoustical energies not associated with rotating stall. 
   
   
     26. A system for correcting rotating stall in a radial diffuser of a centrifugal compressor, the system comprising:
 a sensor, the sensor being configured to measure a parameter representative of acoustical energy associated with rotating stall in a radial diffuser of a centrifugal compressor and generate a sensor signal corresponding to the measured parameter;  
 a high pass filter having a break frequency of 10 Hz, the high pass filter being configured to receive the sensor signal and output a high pass filtered signal;  
 a first low pass filter having a break frequency of 300 Hz, the first low pass filter being configured to receive the high pass filtered signal from the high pass filter and output a low pass filtered signal;  
 a full wave rectifier, the full wave rectifier being configured to receive the low pass filtered signal and output a rectified signal;  
 a second low pass filter, the second low pass filter being configured to receive the rectified signal and output a stall energy component signal; and  
 control circuitry, the control circuitry being configured to determine rotating stall in the radial diffuser using the stall energy component signal and output a control signal to adjust an operational configuration of the centrifugal compressor in response to a determination of rotating stall.  
 
   
   
     27. The system of  claim 26  wherein the sensor comprises a pressure transducer to measure an acoustic pressure in the radial diffuser of the centrifugal compressor with. 
   
   
     28. The system of  claim 27  wherein the pressure transducer is disposed in a discharge passageway of the centrifugal compressor upon installation of the pressure transducer. 
   
   
     29. The system of  claim 26  wherein the high pass filter is a single pole RC high pass filter. 
   
   
     30. The system of  claim 26  wherein the low pass filter is a six order Butterworth low pass filter. 
   
   
     31. The system of  claim 26  further comprising a gain amplifier, the gain amplifier being configured to receive the high pass filtered signal and output an amplified signal to the first low pass filter. 
   
   
     32. The system of  claim 26  wherein the full wave rectifier is an active full wave rectifier. 
   
   
     33. The system of  claim 26  wherein the second low pass filter has a break frequency of 0.16 Hz. 
   
   
     34. The system of  claim 26  wherein:
 the control circuitry comprises a comparator to compare the stall energy component signal to a predetermined value;  
 the control circuitry outputs the control signal in response to the stall energy component signal being greater than the predetermined value; and  
 the predetermined value is a multiple of the stall energy component calculated during normal operation of the centrifugal compressor without rotating stall.  
 
   
   
     35. The system of  claim 34  wherein the predetermined value is 2 to 6 times the value of the stall energy component calculated during normal operation of the centrifugal compressor without rotating stall. 
   
   
     36. A system for correcting rotating stall in a radial diffuser of a centrifugal compressor, the system comprising:
 a sensor, the sensor being configured to measure a parameter representative of acoustical energy associated with rotating stall in a radial diffuser of a centrifugal compressor and generate a sensor signal corresponding to the measured parameter;  
 an analog to digital converter to convert the sensor signal to a digital signal;  
 a digital signal processor, the digital signal processor receiving the digital signal from the digital to analog converter, and the digital signal processor comprising: 
 a high pass filter having a break frequency of 10 Hz, the high pass filter being configured to receive the digital signal and output a high pass filtered signal;  
 a first low pass filter having a break frequency of 300 Hz, the first low pass filter being configured to receive the high pass filtered signal from the high pass filter and output a low pass filtered signal; and  
 a full wave rectifier, the full wave rectifier being configured to receive the low pass filtered signal and output a rectified signal;  
 a second low pass filter, the second low pass filter being configured to receive the rectified signal and output a stall energy component signal;  
 
 a digital to analog converter to convert the stall energy component signal to an analog signal; and  
 control circuitry, the control circuitry being configured to determine rotating stall in the radial diffuser using the analog signal and output a control signal to adjust an operational configuration of the centrifugal compressor in response to a determination of rotating stall.  
 
   
   
     37. The system of  claim 36  wherein the sensor comprises a pressure transducer to measure an acoustic pressure in the radial diffuser of the centrifugal compressor with. 
   
   
     38. The system of  claim 37  wherein the pressure transducer is disposed in a discharge passageway of the centrifugal compressor upon installation of the pressure transducer. 
   
   
     39. The system of  claim 36  further comprising a gain amplifier, the gain amplifier being configured to receive the measured parameter and output an amplified signal to the analog to digital converter. 
   
   
     40. The system of  claim 36  wherein:
 the control circuitry comprises a comparator to compare the stall energy component signal to a predetermined value;  
 the control circuitry outputs the control signal in response to the stall energy component signal being greater than the predetermined value; and  
 the predetermined value is a multiple of the stall energy component calculated during normal operation of the centrifugal compressor without rotating stall.  
 
   
   
     41. The system of  claim 40  wherein the predetermined value is 2 to 6 times the value of the stall energy component calculated during normal operation of the centrifugal compressor without rotating stall.